Construction and characterization of arginine-specific cysteine proteinase (Arg-gingipain)-deficient mutants of Porphyromonas gingivalis. Evidence for significant contribution of Arg-gingipain to virulence

Luteolin inhibits Porphyromonas gingivalis growth and alleviates alveolar bone destruction in experimental murine periodontitis

Periodontal disease is a major oral infectious disease that destroys alveolar bones and causes tooth loss. Porphyromonas gingivalis is a key pathogen that plays a crucial role in periodontitis. In our previous study on the anti-P. gingivalis activity of flavonoid, luteolin, a major flavonoid in edible plants, inhibited the proteolytic activity of gingipains, the major virulence factor in P. gingivalis. This study demonstrated luteolin in vitro and in vivo anti-bacterial activities. Thus, luteolin inhibits planktonic growth and biofilm formation in P. gingivalis. Furthermore, oral administration of luteolin alleviated maxillary alveolar bone resorption (ABR) in murine periodontitis induced by P. gingivalis infection. These results indicate that luteolin may be a potential therapeutic compound that targets P. gingivalis by hindering its growth, biofilm formation, and ABR in the oral cavity.

A conditional gene expression system in Porphyromonas gingivalis for study of the secretion mechanisms of lipoproteins and T9SS cargo proteins

The Gram-negative anaerobe, Porphyromonas gingivalis, is known to be a pathogen associated with chronic periodontitis. P. gingivalis possesses virulence factors such as fimbriae and gingipain proteinases. Fimbrial proteins are secreted to the cell surface as lipoproteins. In contrast, gingipain proteinases are secreted into the bacterial cell surface via the type IX secretion system (T9SS). The transport mechanisms of lipoproteins and T9SS cargo proteins are entirely different and remain unknown. Therefore, using the Tet-on system developed for the genus Bacteroides, we newly created a conditional gene expression system in P. gingivalis. We succeeded in establishing conditional expression of nanoluciferase and its derivatives for lipoprotein export, of FimA for a representative of lipoprotein export, and of T9SS cargo proteins such as Hbp35 and PorA for representatives of type 9 protein export. Using this system, we showed that the lipoprotein export signal, which has recently been found in other species in the phylum Bacteroidota, is also functional in FimA, and that a proton motive force inhibitor can affect type 9 protein export. Collectively, our conditional protein expression method is useful for screening inhibitors of virulence factors, and may be used to investigate the role of proteins essential to bacterial survival in vivo.

Porphyromonas gingivalis Outer Membrane Vesicles Stimulate Gingival Epithelial Cells to Induce Pro-Inflammatory Cytokines via the MAPK and STING Pathways

Porphyromonas gingivalis (Pg) is a keystone pathogen associated with chronic periodontitis and produces outer membrane vesicles (OMVs) that contain lipopolysaccharide (LPS), gingipains, and pathogen-derived DNA and RNA. Pg-OMVs are involved in the pathogenesis of periodontitis. Pg-OMV-activated pathways that induce the production of the pro-inflammatory cytokines, interleukin (IL)-6, and IL-8 in the human gingival epithelial cell line, OBA-9, were investigated. The role of mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB in levels of Pg-OMV-induced pro-inflammatory cytokines was investigated using Western blot analysis and specific pathway inhibitors. Pg-OMVs induced IL-6 and IL-8 production via the extracellular signal-regulated kinase (Erk) 1/2, c-Jun N-terminal kinase (JNK), p38 MAPK, and NF-κB signaling pathways in OBA-9 cells. In addition, the stimulator of interferon genes (STING), an essential innate immune signaling molecule, was triggered by a cytosolic pathogen DNA. Pg-OMV-induced IL-6 and IL-8 mRNA expression and production were significantly suppressed by STING-specific small interfering RNA. Taken together, these results demonstrated that Pg-OMV-activated Erk1/2, JNK, p38 MAPK, STING, and NF-κB signaling pathways resulting in increased IL-6 and IL-8 expression in human gingival epithelial cells. These results suggest that Pg-OMVs may play important roles in periodontitis exacerbation by stimulating various pathways.

Purification of RgpA from external outer membrane vesicles of Porphyromonas gingivalis

INTRODUCTION

Purification of native gingipains is challenging because these proteases are frequently associated with the cell surface, which affects yield. This study aimed to purify native Arg-gingipain (RgpA) from Porphyromonas gingivalis Outer Membrane Vesicles (OMV).

METHODS

Native RgpA was purified from P. gingivalis strain ATCC33277 OMV using a strategy including ultracentrifugation, sonication, and successive anionic and cationic fast protein liquid chromatography (FPLC). The presence and purity of the protease were confirmed by SDS-PAGE and detection of protease activity using fluorogenic substrates. Rat antibodies produced against the unique adhesin hemagglutinin (H1) domain of RgpA (amino acids 719-865) were titrated by ELISA at a 1:100 dilution using whole P. gingivalis lysate as an antigen and western blotting to detect a 75 kDa band corresponding to RgpA.

RESULTS

Double anionic-cationic FLPC yielded prominent peaks with evident amidolytic gingipain activity of the appropriate molecular weight, as confirmed by western blotting. The final RgpA yield from 1 L of bacterial culture with colony forming unit (CFU) (Log₁₀) 7.4 ± 0.08/mL was of 12.6% (2 mg/mL), with 3.2 FU/μg of amidolytic activity.

CONCLUSIONS

This protocol allows purification of native RgpA from OMV that retains protease activity.

Porphyromonas gingivalis Infection Induces Lipopolysaccharide and Peptidoglycan Penetration Through Gingival Epithelium

Periodontal diseases initiate on epithelial surfaces of the subgingival compartment, while the gingival epithelium functions as an epithelial barrier against microbial infection and orchestrates immune responses. Porphyromonas gingivalis is a major pathogen of periodontal diseases and has an ability to penetrate the epithelial barrier. To assess the molecular basis of gingival epithelial barrier dysfunction associated with P. gingivalis, we newly developed a three-dimensional multilayered tissue model of gingival epithelium with gene manipulation. Using this novel approach, P. gingivalis gingipains including Arg- or Lys-specific cysteine proteases were found to specifically degrade junctional adhesion molecule 1 and coxsackievirus and adenovirus receptor in the tissue model, leading to increased permeability for lipopolysaccharide, peptidoglycan, and gingipains. This review summarizes the strategy used by P. gingivalis to disable the epithelial barrier by disrupting specific junctional adhesion molecules.

Porphyromonas gingivalis induces penetration of lipopolysaccharide and peptidoglycan through the gingival epithelium via degradation of coxsackievirus and adenovirus receptor

Porphyromonas gingivalis is a major pathogen of human periodontitis and dysregulates innate immunity at the gingival epithelial surface. We previously reported that the bacterium specifically degrades junctional adhesion molecule 1 (JAM1), causing gingival epithelial barrier breakdown. However, the functions of other JAM family protein(s) in epithelial barrier dysregulation caused by P. gingivalis are not fully understood. The present results show that gingipains, Arg-specific or Lys-specific cysteine proteases produced by P. gingivalis, specifically degrade coxsackievirus and adenovirus receptor (CXADR), a JAM family protein, at R145 and K235 in gingival epithelial cells. In contrast, a gingipain-deficient P. gingivalis strain was found to be impaired in regard to degradation of CXADR. Furthermore, knockdown of CXADR in artificial gingival epithelium increased permeability to dextran 40 kDa, lipopolysaccharide and peptidoglycan, whereas overexpression of CXADR in a gingival epithelial tissue model prevented penetration by those agents following P. gingivalis infection. Together, these results suggest that P. gingivalis gingipains breach the stratified squamous epithelium barrier by degrading CXADR as well as JAM1, which allows for efficient transfer of bacterial virulence factors into subepithelial tissues. TAKEAWAYS: P. gingivalis, a periodontal pathogen, degraded coxsackievirus and adenovirus receptor (CXADR), a JAM family protein, in gingival epithelial tissues. P. gingivalis gingipains, cysteine proteases, degraded CXADR at R145 and K235. CXADR degradation by P. gingivalis caused increased permeability to lipopolysaccharide and peptidoglycan through gingival epithelial tissues.

Invasion of Gingival Epithelial Cells by Porphyromonas gingivalis

Porphyromonas gingivalis is a major pathogen responsible for severe and chronic manifestations of periodontal disease, which is one of the most common infectious disorders of humans. Although human gingival epithelium prevents intrusions by periodontal bacteria, P. gingivalis is able to invade gingival epithelial cells. To study the dynamics and the fate of intracellular P. gingivalis, confocal laser scanning microscopy (CLSM) is a method of choice. Information gained with CLSM contains not only the number of P. gingivalis associated with gingival epithelial cells but also the bacterial localization on/inside the host cells, morphological change of host cells, and physical interaction between the bacteria and host organelle. In this chapter, we describe the protocols for microscopy techniques to morphologically study gingival epithelial cells infected by P. gingivalis.

Ingestion of Porphyromonas gingivalis exacerbates colitis via intestinal epithelial barrier disruption in mice

OBJECTIVE

This study aimed to evaluate the effects of ingested periodontal pathogens on experimental colitis in mice and to elucidate its underlying mechanisms.

BACKGROUND

Inflammatory bowel disease (IBD) is defined as a chronic intestinal inflammation that results in damage to the gastrointestinal tract. Epidemiological studies have shown an association between IBD and periodontitis. Although a large number of ingested oral bacteria reach gastrointestinal tract constantly, the effect of ingested periodontal pathogens on intestinal inflammation is still unknown.

METHODS

Experimental colitis was induced by inclusion of dextran sodium sulfate solution in drinking water of the mice. Major periodontal pathogens (Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum) were administered orally every day during the experiment. The severity of colitis between the groups was compared. In vitro studies of the intestinal epithelial cell line were conducted to explore the molecular mechanisms by which periodontal pathogens affect the development of colitis.

RESULTS

The oral administration of P. gingivalis significantly increased the severity of colitis when compared to other pathogens in the DSS-induced colitis model. The ingested P. gingivalis disrupted the colonic epithelial barrier by decreasing the expression of tight junction proteins in vivo. In vitro permeability assays using the intestinal epithelial cell line suggested the P. gingivalis-specific epithelial barrier disruption. The possible involvement of gingipains in the exacerbation of colitis was implied by using P. gingivalis lacking gingipains.

CONCLUSION

Porphyromonas gingivalis exacerbates gastrointestinal inflammation by directly interacting with the intestinal epithelial barrier in a susceptible host.

Construction and characterization of the PGN_0296 mutant of Porphyromonas gingivalis

The periodontal pathogen Porphyromonas gingivalis produces gingipains (Kgp, RgpA, and RgpB), cysteine proteases involved in the organism's virulence, and pigmentation. We previously showed that deletion of the PGN_0297 and PGN_0300 genes reduced the proteolytic activity of gingipains. The role of the PGN_0296 gene, consisting of an operon with the PGN_0297 and PGN_0300 genes, is unclear. Herein, we examined the effect of PGN_0296 gene deletion on the proteolytic activity. Although the proteolytic activity of the gingipains did not decrease in the culture supernatant of a PGN_0296 gene deletion mutant (ΔPGN_0296), the growth was delayed.

Enzymatic Characteristics and Activities of Gingipains from Porphyromonas gingivalis

Porphyromonas gingivalis is a gram-negative, rod-shaped, nonmotile bacterium belonging to the phylum Bacteroidetes. It produces abundant amounts of proteases in both cell-associated and secretory forms, including a group of cysteine proteases referred to as gingipains, which have attracted much attention due to their high proteolytic activity associated with pathogenicity. Gingipains are grouped into arginine (R)-specific (RgpA and RgpB) and lysine (K)-specific (Kgp) types. Both Rgp (collective term for RgpA and RgpB) and Kgp gingipains play crucial roles in the virulence of P. gingivalis, including the degradation of host periodontal tissues, disruption of host defense mechanisms, and loss of viability in host cells, such as fibroblasts and endothelial cells. In addition to their function in virulence, gingipains are also essential for the growth and survival of P. gingivalis in periodontal pockets through the acquisition of amino acids and heme groups. Furthermore, Rgp and Kgp gingipains are critical in processing fimbriae and several bacterial proteins that contribute to hemagglutination, coaggregation, and hemoglobin binding. This chapter describes the methods used to analyze gingipains.

Outer membrane vesicles of Porphyromonas gingivalis attenuate insulin sensitivity by delivering gingipains to the liver

Outer membrane vesicles (OMVs) are nanosized particles derived from the outer membrane of gram-negative bacteria. Oral bacterium Porphyromonas gingivalis (Pg) is known to be a major pathogen of periodontitis that contributes to the progression of periodontal disease by releasing OMVs. The effect of Pg OMVs on systemic diseases is still unknown. To verify whether Pg OMVs affect the progress of diabetes mellitus, we analyzed the cargo proteins of vesicles and evaluated their effect on hepatic glucose metabolism. Here, we show that Pg OMVs were equipped with Pg-derived proteases gingipains and translocated to the liver in mice. In these mice, the hepatic glycogen synthesis in response to insulin was decreased, and thus high blood glucose levels were maintained. Pg OMVs also attenuated the insulin-induced Akt/glycogen synthase kinase-3 β (GSK-3β) signaling in a gingipain-dependent fashion in hepatic HepG2 cells. These results suggest that the delivery of gingipains mediated by Pg OMV elicits changes in glucose metabolisms in the liver and contributes to the progression of diabetes mellitus.

Porphyromonas gingivalis induces penetration of lipopolysaccharide and peptidoglycan through the gingival epithelium via degradation of junctional adhesion molecule 1

Porphyromonas gingivalis is a major pathogen in severe and chronic manifestations of periodontal disease, which is one of the most common infections of humans. A central feature of P. gingivalis pathogenicity is dysregulation of innate immunity at the gingival epithelial interface; however, the molecular basis underlying P. gingivalis–dependent abrogation of epithelial barrier function remains unknown. Gingival epithelial cells express junctional adhesion molecule (JAM1), a tight junction–associated protein, and JAM1 homodimers regulate epithelial barrier function. Here we show that Arg-specific or Lys-specific cysteine proteases (gingipains) secreted by P. gingivalis can specifically degrade JAM1 at K134 and R234 in gingival epithelial cells, resulting in permeability of the gingival epithelium to 40 kDa dextran, lipopolysaccharide (LPS), and proteoglycan (PGN). A P. gingivalis strain lacking gingipains was impaired in degradation of JAM1. Knockdown of JAM1 in monolayer cells and a three-dimensional multilayered tissue model also increased permeability to LPS, PGN, and gingipains. Inversely, overexpression of JAM1 in epithelial cells prevented penetration by these agents following P. gingivalis infection. Our findings strongly suggest that P. gingivalis gingipains disrupt barrier function of stratified squamous epithelium via degradation of JAM1, allowing bacterial virulence factors to penetrate into subepithelial tissues.

Periodontal diseases, which are among the most common infections of humans, are characterized by gingival inflammation and destruction of the hard and soft tissues that support the tooth, eventually causing tooth loss. Porphyromonas gingivalis is a major pathogen in periodontal diseases. Infection of gingival epithelial cells by P. gingivalis increases epithelial permeability. However, the molecular mechanism and pathological significance of P. gingivalis–dependent barrier dysfunction in human gingival epithelium remain unknown. In this study, we developed a three-dimensional multilayered tissue model of gingival epithelium infected by P. gingivalis and used it to monitor penetration of bacterial products derived from P. gingivalis and other bacteria. We found that P. gingivalis proteases, called gingipains, have a potent and specific ability to degrade JAM1, which regulates epithelial barrier function. Mechanistically, gingipains degrade mature form of JAM1 on the plasma membrane, increasing penetration of 40 kDa dextran, lipopolysaccharide, peptidoglycan, and gingipains. Our study provides new insights into the etiological role of P. gingivalis, leading to periodontal destruction.

A natural anti-periodontitis agent, epimedokoreanin B, inhibits virulence activities of gingipains from Porphyromonas gingivalis

Gingipains are potent virulence cysteine proteases secreted by Porphyromonas gingivalis, a major pathogen of periodontitis. We previously reported that epimedokoreanin B inhibits the activities of gingipains. In this report, we show that epimedokoreanin B inhibits the virulence of gingipains-containing P. gingivalis culture supernatants, indicating the potential use of this prenylated flavonoid as a new agent to combat against periodontal pathogens.

Characterization of the phosphotransacetylase-acetate kinase pathway for ATP production in Porphyromonas gingivalis

Acetyl phosphate (AcP) is generally produced from acetyl coenzyme A by phosphotransacetylase (Pta), and subsequent reaction with ADP, catalyzed by acetate kinase (Ack), produces ATP. The mechanism of ATP production in Porphyromonas gingivalis is poorly understood. The aim of this study was to explore the molecular basis of the Pta-Ack pathway in this microorganism. Pta and Ack from P. gingivalis ATCC 33277 were enzymatically and structurally characterized. Structural and mutational analyses suggest that Pta is a dimer with two substrate-binding sites in each subunit. Ack is also dimeric, with a catalytic cleft in each subunit, and structural analysis indicates a dramatic domain motion that opens and closes the cleft during catalysis. ATP formation by Ack proceeds via a sequential mechanism. Reverse transcription-PCR analysis demonstrated that the pta (PGN_1179) and ack (PGN_1178) genes, tandemly located in the genome, are cotranscribed as an operon. Inactivation of pta or ack in P. gingivalis by homologous recombination was successful only when the inactivated gene was expressed in trans. Therefore, both pta and ack genes are essential for this microorganism. Insights into the Pta-Ack pathway reported herein would be helpful to understand the energy acquisition in P. gingivalis.

PGN_0297 is an essential component of the type IX secretion system (T9SS) in Porphyromonas gingivalis: Tn-seq analysis for exhaustive identification of T9SS-related genes

The type IX secretion system (T9SS) was originally discovered in Porphyromonas gingivalis, one of the pathogenic bacteria associated with periodontal disease and is now known to be present in many members of the phylum Bacteroidetes. The T9SS secretes a number of potent virulence factors, including the highly hydrolytic proteases called gingipains, across the outer membrane in P. gingivalis. To understand the entire machinery of T9SS, an exhaustive search for T9SS‐related genes in P. gingivalis using the mariner family transposon (Tn) and Tn‐seq analysis was performed. Seven hundred and two Tn insertion sites in Tn mutants with no colony pigmentation that is associated with Lys‐gingipain (Kgp) defectiveness were determined, and it was found that the Tn was inserted in the kgp gene and 54 T9SS‐related candidate genes. Thirty‐three out of the 54 genes were already known as T9SS‐related genes. Furthermore, deletion mutant analysis of the remaining 21 genes revealed that they were not related to the T9SS. The 33 T9SS‐related genes include a gene for PGN_0297, which was found to be associated with the T9SS components PorK and PorN. A PGN_0297 gene deletion mutant was constructed, and it was found that the mutant showed no colony pigmentation, hemagglutination or gingipain activities, indicating that PGN_0297 was an essential component of the T9SS. The 33 genes did not include the six genes (gppX, omp17, porY, rfa, sigP and wzx) that were also reported as T9SS‐related genes. gppX deletion and insertion mutants were constructed, and it was found that they did not show deficiency in the T9SS.

Riemerella anatipestifer Type IX Secretion System Is Required for Virulence and Gelatinase Secretion

Riemerella anatipestifer (RA), a major causative agent of septicemia anserum exsudativa in domesticated ducklings, has a protein secretion system known as the type IX secretion system (T9SS). It is unknown whether the T9SS contributes to the virulence of RA through secretion of factors associated with pathogenesis. To answer this question, we constructed an RA mutant deficient in sprT, which encodes a core protein of the T9SS. Deletion of sprT yielded cells that failed to digest gelatin, an effect that was rescued via complementation by a plasmid encoding wild-type sprT. Complement-mediated killing was significantly increased in the deletion mutant, suggesting that proteins secreted by the T9SS are necessary for complement evasion in RA. Liquid chromatography-tandem mass spectrometry analysis revealed that RAYM_01812 and RAYM_04099 proteins containing a subtilisin-like serine protease domain and exhibiting extracellular gelatinase activity were secreted by the T9SS. Animal experiments demonstrated that the virulence of mutant strain ΔsprT strain was attenuated by 42,000-fold relative to wild-type RA-YM. Immunization with the ΔsprT protected ducks from challenge with RA-YM, suggesting that the former can be used as a live attenuated vaccine. These results indicate that the T9SS is functional in RA and contributes to its virulence by exporting key proteins. In addition, subtilisin-like serine proteases which are important virulence factors that interact with complement proteins may enable RA to evade immune surveillance in the avian innate immune system.

Effect of extracytoplasmic function sigma factors on autoaggregation, hemagglutination, and cell surface properties of Porphyromonas gingivalis

Porphyromonas gingivalis is a bacterium frequently isolated from chronic periodontal lesions and is involved in the development of chronic periodontitis. To colonize the gingival crevice, P. gingivalis has to adapt to environmental stresses. Microbial gene expression is regulated by transcription factors such as those in two-component systems and extracytoplasmic function (ECF) sigma factors. ECF sigma factors are involved in the regulation of environmental stress response genes; however, the roles of individual ECF sigma factors are largely unknown. The purpose of this study was to investigate the functions, including autoaggregation, hemagglutination, gingipain activity, susceptibility to antimicrobial agents, and surface structure formation, of P. gingivalis ECF sigma factors encoded by SigP (PGN_0274), SigCH (PGN_0319), PGN_0450, PGN_0970, and SigH (PGN_1740). Various physiological aspects of the sigP mutant were affected; autoaggregation was significantly decreased at 60 min (p < 0.001), hemagglutination activity was markedly reduced, and enzymatic activities of Kgp and Rgps were significantly decreased (p < 0.001). The other mutants also showed approximately 50% reduction in Rgps activity. Kgp activity was significantly reduced in the sigH mutant (p < 0.001). No significant differences in susceptibilities to tetracycline and ofloxacin were observed in the mutants compared to those of the wild-type strain. However, the sigP mutant displayed an increased susceptibility to ampicillin, whereas the PGN_0450 and sigH mutants showed reduced susceptibility. Transmission electron microscopy images revealed increased levels of outer membrane vesicles formed at the cell surfaces of the sigP mutant. These results indicate that SigP is important for bacterial surface-associated activities, including gingipain activity, autoaggregation, hemagglutination, vesicle formation, and antimicrobial susceptibility.

PorV is an Outer Membrane Shuttle Protein for the Type IX Secretion System

Porphyromonas gingivalis is a keystone pathogen associated with chronic periodontitis. Major virulence factors named gingipains (cysteine proteinases, RgpA, RgpB and Kgp) are secreted via the Type IX Secretion System (T9SS). These, together with approximately 30 other proteins, are secreted to the cell surface and anchored to the outer membrane by covalent modification to anionic lipopolysaccharide (A-LPS) via the novel Gram negative sortase, PorU. PorU is localised on the cell surface and cleaves the C-terminal domain signal (CTD) of T9SS substrates and conjugates their new C-termini to A-LPS. A 440 kDa-attachment complex was identified in the wild-type (WT) comprising of PorU:PorV:PorQ:PorZ. In mutant strains, sub-complexes comprising PorU:PorV or PorQ:PorZ were also identified at smaller native sizes suggesting that PorU and PorZ are anchored to the cell surface via interaction with the PorV and PorQ outer membrane proteins, respectively. Analysis of porU mutants and a CTD cleavage mutant revealed accumulation of immature T9SS substrates in a PorV-bound form. Quantitative label-free proteomics of WT whole cell lysates estimated that the proportion of secretion channels:attachment complexes:free PorV:T9SS substrates was 1:6:110:2000 supporting a role for PorV as a shuttle protein delivering secreted proteins to the attachment complex for CTD signal cleavage and A-LPS modification.

Mechanisms by which Porphyromonas gingivalis evades innate immunity

The oral cavity is home to unique resident microbial communities whose interactions with host immunity are less frequently studied than those of the intestinal microbiome. We examined the stimulatory capacity and the interactions of two oral bacteria, Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum), on Dendritic Cell (DC) activation, comparing them to the effects of the well-studied intestinal microbe Escherichia coli (E. coli). Unlike F. nucleatum and E. coli, P. gingivalis failed to activate DCs, and in fact silenced DC responses induced by F. nucleatum or E. coli. We identified a variant strain of P. gingivalis (W50) that lacked this immunomodulatory activity. Using biochemical approaches and whole genome sequencing to compare the two substrains, we found a point mutation in the hagA gene. This protein is though to be involved in the alteration of the PorSS/gingipain pathway, which regulates protein secretion into the extracellular environment. A proteomic comparison of the secreted products of the two substrains revealed enzymatic differences corresponding to this phenotype. We found that P. gingivalis secretes gingipain(s) that inactivate several key proinflammatory mediators made by DCs and/or T cells, but spare Interleukin-1 (IL-1) and GM-CSF, which can cause capillary leaks that serve as a source of the heme that P. gingivalis requires for its survival, and GM-CSF, which can cause epithelial-cell growth. Taken together, our results suggest that P. gingivalis has evolved potent mechanisms to modulate its virulence factors and dampen the innate immune response by selectively inactivating most proinflammatory cytokines.

Diurnal dynamic behavior of microglia in response to infected bacteria through the UDP-P2Y6 receptor system

It has long been believed that microglia morphologically transform into the activated state by retracting their long processes and consuming pathogens when bacteria infect into the brain parenchyma. In the present study, however, we showed for the first time that murine cortical microglia extend their processes towards focally injected Porphyromonas gingivalis. This P. gingivalis-induced microglial process extension was significantly increased during the light (sleeping) phase than the dark (waking) phase. In contrast, focally injected ATP-induced microglial process extension was significantly increased during the dark phase than the light phase. Furthermore, in contrast to the P2Y₁₂ receptor-mediated mechanism of ATP-induced microglial process extension, the P. gingivalis-mediated microglial process extension was mediated by P2Y₆ receptors. The infection of bacteria such as P. gingivalis to the brain parenchyma may induce the secretion of UDP from microglia at the site of infection, which in turn induces the process extension of the neighboring microglia.

Role of Mfa5 in Expression of Mfa1 Fimbriae in Porphyromonas gingivalis

Fimbriae are protein-based filamentous appendages that protrude from the bacterial cell surface and facilitate host adhesion. Two types of fimbriae, FimA and Mfa1, of the periodontal pathogen Porphyromonas gingivalis are responsible for adherence to other bacteria and to host cells in the oral cavity. Both fimbrial forms are composed of 5 proteins, but there is limited information about their polymerization mechanisms. Here, the authors evaluated the function of Mfa5, one of the Mfa1 fimbrial accessory proteins. Using mfa5 gene disruption and complementation studies, the authors revealed that Mfa5 affects the incorporation of other accessory proteins, Mfa3 and Mfa4, into fibers and the expression of fimbriae on the cell surface. Mfa5 is predicted to have a C-terminal domain (CTD) that uses the type IX secretion system (T9SS), which is limited to this organism and related Bacteroidetes species, for translocation across the outer membrane. To determine the relationship between the putative Mfa5 CTD and the T9SS, mutants were constructed with in-frame deletion of the CTD and deletion of porU, a C-terminal signal peptidase linked to T9SS-mediated secretion. The ∆CTD-expressing strain presented a similar phenotype to the mfa5 disruption mutant with reduced expression of fimbriae lacking all accessory proteins. The ∆porU mutants and the ∆CTD-expressing strain showed intracellular accumulation of Mfa5. These results indicate that Mfa5 function requires T9SS-mediated translocation across the outer membrane, which is dependent on the CTD, and subsequent incorporation into fibers. These findings suggest the presence of a novel polymerization mechanism of the P. gingivalis fimbriae.

Lipid droplets affect elimination of Porphyromonas gingivalis in HepG2 cells by altering the autophagy-lysosome system

Recent studies have shown that infection with Porphyromonas gingivalis, a major periodontal pathogen, hastens the progression of non-alcoholic fatty liver disease (NAFLD). However, the intracellular fate of P. gingivalis in hepatocytes remains unknown. Here, using oleic-acid-induced HepG2 cells as an in vitro model for NAFLD, we found that lipid droplets increased the existence of P. gingivalis in the cells at an early phase of infection. Confocal microscopic analysis revealed that lipid droplets affected the formation of autolysosomes in infected cells. Thus, lipid droplets affect the elimination of P. gingivalis in HepG2 cells by altering the autophagy-lysosome system.

Apple- and Hop-Polyphenols Inhibit Porphyromonas gingivalis-Mediated Precursor of Matrix Metalloproteinase-9 Activation and Invasion of Oral Squamous Cell Carcinoma Cells

BACKGROUND

Recent epidemiologic studies have revealed a significant association between periodontitis and oral squamous cell carcinoma (OSCC). Furthermore, periodontitis is markedly associated with orodigestive cancer mortality, whereas Porphyromonas gingivalis (Pg) infection has been identified as a specific and potentially independent microbial factor related to increased risk of orodigestive cancer death. The authors previously reported that Pg induced the precursor form of matrix metalloproteinase-9 (proMMP-9) production via proteinase-activated receptor (PAR)-related pathways, after which proMMP-9 was activated by gingipains to enhance cellular invasion of SAS cells. In the present study, effects of selected polyphenols as inhibitors of cellular invasion caused by Pg gingipains in SAS cells are examined.

METHODS

OSCC cells were infected with Pg strains including gingipain mutants. To evaluate effects of inhibitors: 1) apple polyphenol (AP); 2) hop bract polyphenol (HBP); 3) high-molecular-weight fractions of HBP (HMW-HBP); 4) low-molecular-weight fractions of HBP (LMW-HBP); 5) epigallocatechin gallate (EGCg); 6) KYT-1 (Arg-gingipain inhibitor); and KYT-36 (Lys-gingipain inhibitor) in combination are used. PAR2 and PAR4 mRNA expressions are examined using real-time reverse transcription polymerase chain reaction, and signaling pathways are evaluated by western blotting analysis.

RESULTS

KYT-1/KYT-36, AP, HBP, and HMW-HBP significantly inhibited PAR2 and PAR4 mRNA expressions, proMMP-9 activation, and cellular invasion. Furthermore, AP, HBP, and HMW-HBP reduced activation of heat shock protein 27 and Ets1 and nuclear translocation of nuclear factor-kappa B, whereas EGCg and LMW-HBP did not.

CONCLUSION

These results suggest that AP, HBP, HMW-HBP are potent inhibitors of proMMP-9 activation and cellular invasion mediated with Pg in OSCC cells.

A two-component system regulates gene expression of the type IX secretion component proteins via an ECF sigma factor

The periodontopathogen Porphyromonas gingivalis secretes potent pathogenic proteases, gingipains, via the type IX secretion system (T9SS). This system comprises at least 11 components; however, the regulatory mechanism of their expression has not yet been elucidated. Here, we found that the PorY (PGN_2001)-PorX (PGN_1019)-SigP (PGN_0274) cascade is involved in the regulation of T9SS. Surface plasmon resonance (SPR) analysis revealed a direct interaction between a recombinant PorY (rPorY) and a recombinant PorX (rPorX). rPorY autophosphorylated and transferred a phosphoryl group to rPorX in the presence of Mn²⁺. These results demonstrate that PorX and PorY act as a response regulator and a histidine kinase, respectively, of a two component system (TCS), although they are separately encoded on the chromosome. T9SS component-encoding genes were down-regulated in a mutant deficient in a putative extracytoplasmic function (ECF) sigma factor, PGN_0274 (SigP), similar to the porX mutant. Electrophoretic gel shift assays showed that rSigP bound to the putative promoter regions of T9SS component-encoding genes. The SigP protein was lacking in the porX mutant. Co-immunoprecipitation and SPR analysis revealed the direct interaction between SigP and PorX. Together, these results indicate that the PorXY TCS regulates T9SS-mediated protein secretion via the SigP ECF sigma factor.

Acyl-CoA reductase PGN_0723 utilizes succinyl-CoA to generate succinate semialdehyde in a butyrate-producing pathway of Porphyromonas gingivalis

The molecular basis of butyrate production in Porphyromonas gingivalis has not been fully elucidated, even though butyrate, a short chain fatty acid (SCFA), can exert both beneficial and harmful effects on a mammalian host. A database search showed that the amino acid sequence of PGN_0723 protein was 50.6% identical with CoA-dependent succinate semialdehyde dehydrogenase (SSADH) in Clostridium kluyveri. By contrast, the protein has limited identity (19.1%) with CoA-independent SSADH in Escherichia coli. Compared with the wild type, growth speed, and final turbidity were lower in the PGN_0723 deletion strain that was constructed by replacing the PGN_0723 gene with an erythromycin resistance cassette. Gas chromatography mass spectrometry revealed the supernatant concentrations of the SCFAs butyrate, isobutyrate, and isovalerate, but not propionate, in the PGN_0723 deletion strain were also lower than those in the wild type. The wild-type phenotype was restored in a complemented strain. We cloned the PGN_0723 gene, purified the recombinant protein, and computationally constructed its three-dimensional model. A colorimetric assay and liquid chromatography-tandem mass spectrometry analysis demonstrated that the recombinant PGN_0723 produces succinate semialdehyde, which is an intermediate in the P. gingivalis butyrate synthesis pathway, not from succinate but from succinyl-CoA in the presence of NAD(P)H via a ping-pong bi-bi mechanism. Asn110Ala and Cys239Ala mutations resulted in a significant loss of the CoA-dependent PGN_0723 enzymatic activity. The study provides new insights into butyrate production, which constitutes a virulence factor in P. gingivalis.

Structure of the fimbrial protein Mfa4 from Porphyromonas gingivalis in its precursor form: implications for a donor-strand complementation mechanism

Gingivitis and periodontitis are chronic inflammatory diseases that can lead to tooth loss. One of the causes of these diseases is the Gram-negative Porphyromonas gingivalis. This periodontal pathogen is dependent on two fimbriae, FimA and Mfa1, for binding to dental biofilm, salivary proteins, and host cells. These fimbriae are composed of five proteins each, but the fimbriae assembly mechanism and ligands are unknown. Here we reveal the crystal structure of the precursor form of Mfa4, one of the accessory proteins of the Mfa1 fimbria. Mfa4 consists of two β-sandwich domains and the first part of the structure forms two well-defined β-strands that run over both domains. This N-terminal region is cleaved by gingipains, a family of proteolytic enzymes that encompass arginine- and lysine-specific proteases. Cleavage of the N-terminal region generates the mature form of the protein. Our structural data allow us to propose that the new N-terminus of the mature protein may function as a donor strand in the polymerization of P. gingivalis fimbriae.

Heme acquisition mechanisms of Porphyromonas gingivalis - strategies used in a polymicrobial community in a heme-limited host environment

Porphyromonas gingivalis, a main etiologic agent and key pathogen responsible for initiation and progression of chronic periodontitis requires heme as a source of iron and protoporphyrin IX for its survival and the ability to establish an infection. Porphyromonas gingivalis is able to accumulate a defensive cell-surface heme-containing pigment in the form of μ-oxo bisheme. The main sources of heme for P. gingivalis in vivo are hemoproteins present in saliva, gingival crevicular fluid, and erythrocytes. To acquire heme, P. gingivalis uses several mechanisms. Among them, the best characterized are those employing hemagglutinins, hemolysins, and gingipains (Kgp, RgpA, RgpB), TonB-dependent outer-membrane receptors (HmuR, HusB, IhtA), and hemophore-like proteins (HmuY, HusA). Proteins involved in intracellular heme transport, storage, and processing are less well characterized (e.g. PgDps). Importantly, P. gingivalis may also use the heme acquisition systems of other bacteria to fulfill its own heme requirements. Porphyromonas gingivalis displays a novel paradigm for heme acquisition from hemoglobin, whereby the Fe(II)-containing oxyhemoglobin molecule must first be oxidized to methemoglobin to facilitate heme release. This process not only involves P. gingivalis arginine- and lysine-specific gingipains, but other proteases (e.g. interpain A from Prevotella intermedia) or pyocyanin produced by Pseudomonas aeruginosa. Porphyromonas gingivalis is then able to fully proteolyze the more susceptible methemoglobin substrate to release free heme or to wrest heme from it directly through the use of the HmuY hemophore.

Epithelial cell detachment by Porphyromonas gingivalis biofilm and planktonic cultures

Porphyromonas gingivalis is present as a biofilm at the sites of periodontal infections. The detachment of gingival epithelial cells induced by P. gingivalis biofilms was examined using planktonic cultures as a comparison. Exponentially grown planktonic cultures or 40-h biofilms were co-incubated with epithelial cells in a 24-well plate for 4 h. Epithelial cell detachment was assessed using imaging. The activity of arginine-gingipain (Rgp) and gene expression profiles of P. gingivalis cultures were examined using a gingipain assay and quantitative PCR, respectively. P. gingivalis biofilms induced significantly higher cell detachment and displayed higher Rgp activity compared to the planktonic cultures. The genes involved in gingipain post-translational modification, but not rgp genes, were significantly up-regulated in P. gingivalis biofilms. The results underline the importance of including biofilms in the study of bacterial and host cell interactions.

Involvement of an Skp-Like Protein, PGN_0300, in the Type IX Secretion System of Porphyromonas gingivalis

The oral Gram-negative anaerobic bacterium Porphyromonas gingivalis is an important pathogen involved in chronic periodontitis. Among its virulence factors, the major extracellular proteinases, Arg-gingipain and Lys-gingipain, are of interest given their abilities to degrade host proteins and process other virulence factors. Gingipains possess C-terminal domains (CTDs) and are translocated to the cell surface or into the extracellular milieu by the type IX secretion system (T9SS). Gingipains contribute to the colonial pigmentation of the bacterium on blood agar. In this study, Omp17, the PGN_0300 gene product, was found in the outer membrane fraction. A mutant lacking Omp17 did not show pigmentation on blood agar and showed reduced proteolytic activity of the gingipains. CTD-containing proteins were released from bacterial cells without cleavage of the CTDs in the omp17 mutant. Although synthesis of the anionic polysaccharide (A-LPS) was not affected in the omp17 mutant, the processing of and A-LPS modification of CTD-containing proteins was defective. PorU, a C-terminal signal peptidase that cleaves the CTDs of other CTD-containing proteins, was not detected in any membrane fraction of the omp17 mutant, suggesting that the defective maturation of CTD-containing proteins by impairment of Omp17 is partly due to loss of function of PorU. In the mouse subcutaneous infection experiment, the omp17 mutant was less virulent than the wild type. These results suggested that Omp17 is involved in P. gingivalis virulence.

Mfa4, an Accessory Protein of Mfa1 Fimbriae, Modulates Fimbrial Biogenesis, Cell Auto-Aggregation, and Biofilm Formation in Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative obligate anaerobic bacterium, is considered to be a key pathogen in periodontal disease. The bacterium expresses Mfa1 fimbriae, which are composed of polymers of Mfa1. The minor accessory components Mfa3, Mfa4, and Mfa5 are incorporated into these fimbriae. In this study, we characterized Mfa4 using genetically modified strains. Deficiency in the mfa4 gene decreased, but did not eliminate, expression of Mfa1 fimbriae. However, Mfa3 and Mfa5 were not incorporated because of defects in posttranslational processing and leakage into the culture supernatant, respectively. Furthermore, the mfa4-deficient mutant had an increased tendency to auto-aggregate and form biofilms, reminiscent of a mutant completely lacking Mfa1. Notably, complementation of mfa4 restored expression of structurally intact and functional Mfa1 fimbriae. Taken together, these results indicate that the accessory proteins Mfa3, Mfa4, and Mfa5 are necessary for assembly of Mfa1 fimbriae and regulation of auto-aggregation and biofilm formation of P. gingivalis. In addition, we found that Mfa3 and Mfa4 are processed to maturity by the same RgpA/B protease that processes Mfa1 subunits prior to polymerization.

Gingipains from the Periodontal Pathogen Porphyromonas gingivalis Play a Significant Role in Regulation of Angiopoietin 1 and Angiopoietin 2 in Human Aortic Smooth Muscle Cells

Angiopoietin 1 (Angpt1) and angiopoietin 2 (Angpt2) are the ligands of tyrosine kinase (Tie) receptors, and they play important roles in vessel formation and the development of inflammatory diseases, such as atherosclerosis. Porphyromonas gingivalis is a Gram-negative periodontal bacterium that is thought to contribute to the progression of cardiovascular disease. The aim of this study was to investigate the role of P. gingivalis infection in the modulation of Angpt1 and Angpt2 in human aortic smooth muscle cells (AoSMCs). We exposed AoSMCs to wild-type (W50 and 381), gingipain mutant (E8 and K1A), and fimbrial mutant (DPG-3 and KRX-178) P. gingivalis strains and to different concentrations of tumor necrosis factor (TNF). The atherosclerosis risk factor TNF was used as a positive control in this study. We found that P. gingivalis (wild type, K1A, DPG3, and KRX178) and TNF upregulated the expression of Angpt2 and its transcription factor ETS1, respectively, in AoSMCs. In contrast, Angpt1 was inhibited by P. gingivalis and TNF. However, the RgpAB mutant E8 had no effect on the expression of Angpt1, Angpt2, or ETS1 in AoSMCs. The results also showed that ETS1 is critical for P. gingivalis induction of Angpt2. Exposure to Angpt2 protein enhanced the migration of AoSMCs but had no effect on proliferation. This study demonstrates that gingipains are crucial to the ability of P. gingivalis to markedly increase the expressed Angpt2/Angpt1 ratio in AoSMCs, which determines the regulatory role of angiopoietins in angiogenesis and their involvement in the development of atherosclerosis. These findings further support the association between periodontitis and cardiovascular disease.

The impact of virulence factors of Porphyromonas gingivalis on wound healing in vitro

Background

Porphyromonas gingivalis inhibits oral epithelial wound healing in vitro more strongly than other oral bacteria, but it is unknown why P. gingivalis is such a potent inhibitor of wound healing.

Objective

Therefore, the aim of this study was to investigate the influence of major virulence factors of P. gingivalis on wound healing in an in vitro wound-healing model. The influence of the capsular polysaccharide, the Arg- and Lys- gingipains, the major fimbriae and lipopolysaccharide (LPS) was investigated.

Design

A standardized scratch was made in a confluent layer of human oral epithelial cells HO-1-N-1. The epithelial cells were then challenged with different concentrations of several P. gingivalis wild-type strains and knockout mutants. Closure of the scratch was determined after 17 h and compared to control conditions without bacteria.

Results

The P. gingivalis strains ATCC 33277, W83, and W50 significantly inhibited wound healing. The presence of a capsular polysaccharide lowered significantly the inhibition of epithelial cell migration, while gingipain activity significantly increased the inhibition of cell migration. LPS and the major fimbriae did not influence epithelial cell migration. None of the tested P. gingivalis strains completely prevented the inhibition of cell migration, suggesting that other characteristics of P. gingivalis also play a role in the inhibition of wound healing, and that further research is needed.

Conclusions

The capsular polysaccharide and the Arg- and Lys- gingipains of P. gingivalis influenced the capacity of P. gingivalis to hinder wound healing, while LPS and the major fimbriae had no effect.

Structural and mutational analyses of dipeptidyl peptidase 11 from Porphyromonas gingivalis reveal the molecular basis for strict substrate specificity

The dipeptidyl peptidase 11 from Porphyromonas gingivalis (PgDPP11) belongs to the S46 family of serine peptidases and preferentially cleaves substrates with Asp/Glu at the P1 position. The molecular mechanism underlying the substrate specificity of PgDPP11, however, is unknown. Here, we report the crystal structure of PgDPP11. The enzyme contains a catalytic domain with a typical double β-barrel fold and a recently identified regulatory α-helical domain. Crystal structure analyses, docking studies, and biochemical studies revealed that the side chain of Arg673 in the S1 subsite is essential for recognition of the Asp/Glu side chain at the P1 position of the bound substrate. Because S46 peptidases are not found in mammals and the Arg673 is conserved among DPP11s, we anticipate that DPP11s could be utilised as targets for antibiotics. In addition, the present structure analyses could be useful templates for the design of specific inhibitors of DPP11s from pathogenic organisms.

Noncanonical activation of β-catenin by Porphyromonas gingivalis

Porphyromonas gingivalis is an established pathogen in periodontal disease and an emerging pathogen in serious systemic conditions, including some forms of cancer. We investigated the effect of P. gingivalis on β-catenin signaling, a major pathway in the control of cell proliferation and tumorigenesis. Infection of gingival epithelial cells with P. gingivalis did not influence the phosphorylation status of β-catenin but resulted in proteolytic processing. The use of mutants deficient in gingipain production, along with gingipain-specific inhibitors, revealed that gingipain proteolytic activity was required for β-catenin processing. The β-catenin destruction complex components Axin1, adenomatous polyposis coli (APC), and GSK3β were also proteolytically processed by P. gingivalis gingipains. Cell fractionation and Western blotting demonstrated that β-catenin fragments were translocated to the nucleus. The accumulation of β-catenin in the nucleus following P. gingivalis infection was confirmed by immunofluorescence microscopy. A luciferase reporter assay showed that P. gingivalis increased the activity of the β-catenin-dependent TCF/LEF promoter. P. gingivalis did not increase Wnt3a mRNA levels, a finding consistent with P. gingivalis-induced proteolytic processing causing the increase in TCF/LEF promoter activity. Thus, our data indicate that P. gingivalis can induce the noncanonical activation of β-catenin and disassociation of the β-catenin destruction complex by gingipain-dependent proteolytic processing. β-Catenin activation in epithelial cells by P. gingivalis may contribute to a proliferative phenotype.

Role of extracytoplasmic function sigma factors in biofilm formation of Porphyromonas gingivalis

Background

Porphyromonas gingivalis has been implicated as a major pathogen in the development and progression of chronic periodontitis. P. gingivalis biofilm formation in the subgingival crevice plays an important role in the ability of the bacteria to tolerate stress signals outside the cytoplasmic membrane. Some bacteria use a distinct subfamily of sigma factors to regulate their extracytoplasmic functions (the ECF subfamily). The objective of this study was to determine if P. gingivalis ECF sigma factors affect P. gingivalis biofilm formation.

Methods

To elucidate the role of ECF sigma factors in P. gingivalis, chromosomal mutants carrying a disruption of each ECF sigma factor-encoding gene were constructed. Bacterial growth curves were measured by determining the turbidity of bacterial cultures. The quantity of biofilm growing on plates was evaluated by crystal violet staining.

Results

Comparison of the growth curves of wild-type P. gingivalis strain 33277 and the ECF mutants indicated that the growth rate of the mutants was slightly lower than that of the wild-type strain. The PGN_0274- and PGN_1740-defective mutants had increased biofilm formation compared with the wild-type (p < 0.001); however, the other ECF sigma factor mutants or the complemented strains did not enhance biofilm formation.

Conclusion

These results suggest that PGN_0274 and PGN_1740 play a key role in biofilm formation by P. gingivalis.

Electronic supplementary material

The online version of this article (doi:10.1186/1472-6831-15-4) contains supplementary material, which is available to authorized users.

Attenuation of the phosphatidylinositol 3-kinase/Akt signaling pathway by Porphyromonas gingivalis gingipains RgpA, RgpB, and Kgp

Porphyromonas gingivalis is a major pathogen of periodontal diseases, including periodontitis. We have investigated the effect of P. gingivalis infection on the PI3K/Akt (protein kinase B) signaling pathway in gingival epithelial cells. Here, we found that live P. gingivalis, but not heat-killed P. gingivalis, reduced Akt phosphorylation at both Thr-308 and Ser-473, which implies a decrease in Akt activity. Actually, PI3K, which is upstream of Akt, was also inactivated by P. gingivalis. Furthermore, glycogen synthase kinase 3α/β, mammalian target of rapamycin, and Bad, which are downstream proteins in the PI3K/Akt cascade, were also dephosphorylated, a phenomenon consistent with Akt inactivation by P. gingivalis. However, these events did not require direct interaction between bacteria and host cells and were independent of P. gingivalis invasion into the cells. The use of gingipain-specific inhibitors and a gingipain-deficient P. gingivalis mutant KDP136 revealed that the gingipains and their protease activities were essential for the inactivation of PI3K and Akt. The associations between the PI3K regulatory subunit p85α and membrane proteins were disrupted by wild-type P. gingivalis. Moreover, PDK1 translocation to the plasma membrane was reduced by wild-type P. gingivalis, but not KDP136, indicating little production of phosphatidylinositol 3,4,5-triphosphate by PI3K. Therefore, it is likely that PI3K failed to transmit homeostatic extracellular stimuli to intracellular signaling pathways by gingipains. Taken together, our findings indicate that P. gingivalis attenuates the PI3K/Akt signaling pathway via the proteolytic effects of gingipains, resulting in the dysregulation of PI3K/Akt-dependent cellular functions and the destruction of epithelial barriers.

kgp, rgpA, and rgpB DNA vaccines induce antibody responses in experimental peri-implantitis

BACKGROUND

Peri-implantitis is the key factor for implant failure. This study aims to evaluate kgp, rgpA, and rgpB DNA vaccines to induce an immune response and prevent peri-implantitis.

METHODS

The kgp, rgpA, and rgpB genes were amplified by polymerase chain reaction (PCR) from Porphyromonas gingivalis (Pg) ATCC 33277 and cloned into the pVAX1 vector. Titanium implants were placed into the mandibular bone of dogs. Three months later, the animals were divided into four groups, immunized with pVAX1-kgp, pVAX1-rgpA, pVAX1-rgpB, or pVAX1. Cotton ligatures infiltrated with Pg were tied around the neck of the implants. Immunoglobulin (Ig)G and IgA antibodies were detected by enzyme-linked immunosorbent assay before and after immunization.

RESULTS

The kgp, rgpA, and rgpB genes were successfully cloned into the pVAX1 plasmid. Animals immunized with pVAX1-kgp and pVAX1-rgpA showed higher titers of IgG and IgA antibodies compared to those before immunization (P <0.05) and compared to those that were immunized with pVAX1 and pVAX1-rgpB, whereas there were no significant differences in the animals treated with pVAX1 and pVAX1-rgpB. Furthermore, among these, the kgp DNA vaccine was more effective. The bone losses of the groups with pVAX1-kgp and pVAX1-rgpA were significantly attenuated.

CONCLUSION

pVAX1-kgp and pVAX1-rgpA DNA vaccines enhanced immunity responses and significantly retarded bone loss in experimental peri-implantitis animal models, whereas pVAX1-rgpB was ineffective.

Analysis of a Lys-specific serine endopeptidase secreted via the type IX secretion system in Porphyromonas gingivalis

Porphyromonas gingivalis, a significant causative agent of adult periodontitis, possesses a novel secretion system called the type IX secretion system (T9SS). A number of virulence factors, such as Arg-gingipain (Rgp), are translocated onto the cell surface and into the extracellular milieu via the T9SS. In this study, we found that the PGN_1416 90- to 120-kDa diffuse protein bands were located in the outer membrane fraction and that the presence of the bands was dependent on genes involved in the T9SS and the formation of anionic lipopolysaccharide (A-LPS). These data strongly suggest that the PGN_1416 protein is secreted by the T9SS and anchored onto the cell surface by binding to A-LPS. Enzymatic analysis using outer membrane fractions suggested that the PGN_1416 protein has a Lys-specific serine endopeptidase activity and that its activation requires processing by Rgp. Homologues of the gene encoding PGN_1416, which is referred to as pepK, were found in bacteria belonging to the phyla Bacteroidetes and Proteobacteria, whereas homologues encoding the C-terminal domain, which is essential for T9SS-mediated secretion, and the catalytic domain were only observed in bacteria belonging to the Bacteroidetes phylum.

Porphyromonas gingivalis gingipain is involved in the detachment and aggregation of Aggregatibacter actinomycetemcomitans biofilm

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are major periodontal pathogens that cause several types of periodontal disease. Our previous study suggested that P. gingivalis gingipains secreted in the subgingival environment are related to the detachment of A.actinomycetemcomitans biofilms. However, it remains unclear whether arginine-specific cysteine proteinase (Rgp) and lysine-specific proteinase (Kgp) play different roles in the detachment of A. actinomycetemcomitans biofilm. The aim of this study was to investigate possible disruptive roles of Kgp and Rgp in the aggregation and attachment of A. actinomycetemcomitans. While P. gingivalis ATCC33277 culture supernatant has an ability to decrease autoaggregation and coaggregation of A. actinomycetemcomitans cells, neither the boiled culture supernatant of ATCC33277 nor the culture supernatant of KDP136 showed this ability. The addition of KYT-1 and KYT-36, specific inhibitors of Rgp and Kgp, respectively, showed no influence on the ability of P. gingivalis culture supernatant. The result of gelatin zymography suggested that other proteases processed by gingipains mediated the decrease of A. actinomycetemcomitans aggregations. We also examined the biofilm-destructive effect of gingipains by assessing the detachment of A. actinomycetemcomitans from polystyrene surfaces. Scanning electron microscope analysis indicated that A. actinomycetemcomitans cells were detached by P. gingivalis Kgp. The quantity of A. actinomycetemcomitans in biofilm was decreased in co-culture with P. gingivalis. However, this was not found after the addition of KYT-36. These findings suggest that Kgp is a critical component for the detachment and decrease of A. actinomycetemcomitans biofilms.

Hemoglobin receptor protein from Porphyromonas gingivalis induces interleukin-8 production in human gingival epithelial cells through stimulation of the mitogen-activated protein kinase and NF-κB signal transduction pathways

Periodontitis is an inflammatory disease of polymicrobial origin affecting the tissues supporting the tooth. The oral anaerobic bacterium Porphyromonas gingivalis, which is implicated as an important pathogen for chronic periodontitis, triggers a series of host inflammatory responses that promote the destruction of periodontal tissues. Among the virulence factors of P. gingivalis, hemoglobin receptor protein (HbR) is a major protein found in culture supernatants. In this study, we investigated the roles of HbR in the production of inflammatory mediators. We found that HbR induced interleukin-8 (IL-8) production in the human gingival epithelial cell line Ca9-22. p38 mitogen-activated protein kinase (MAPK) and extracellular signal-related kinase 1/2 (Erk1/2) were activated in HbR-stimulated Ca9-22 cells. Inhibitors of p38 MAPK (SB203580) and Erk1/2 (PD98059) blocked HbR-induced IL-8 production. Additionally, HbR stimulated the translocation of NF-κB-p65 to the nucleus, consistent with enhancement of IL-8 expression by activation of the NF-κB pathway. In addition, small interfering RNA (siRNA) targeting activating transcription factor 2 (ATF-2) or cyclic AMP-response element-binding protein (CREB) inhibited HbR-induced IL-8 production. Moreover, pretreatment with SB203580 and PD98059 reduced HbR-induced phosphorylation of CREB and ATF-2, respectively. Combined pretreatment with an inhibitor of NF-κB (BAY11-7082) and SB203580 was more efficient in inhibiting the ability of HbR to induce IL-8 production than pretreatment with either BAY11-7082 or SB203580 alone. Thus, in Ca9-22 cells, the direct activation of p38 MAPK and Erk1/2 by HbR caused the activation of the transcription factors ATF-2, CREB, and NF-κB, thus resulting in the induction of IL-8 production.